1. Field of the Invention
The present invention relates to a process for producing a fatty acid ester and glycerol by reacting an oil or fat with an alcohol, and to a fuel comprising a fatty acid ester obtained by the above process.
2. Description of Related Art
A principal component of the oil or fat is esters composed of a fatty acid and glycerol, called triglycerides. Fatty acid esters obtained by transesterification of an oil or fat with an alcohol have found wide applications as industrial raw materials, pharmaceuticals and so on.
Processes have been described for manufacturing fuels for diesel engine or base oils for lubricant oil containing fatty acid esters as substitutes for the conventional mineral oils, by transesterification of an oil or fat with an alcohol. For example, in JP-A-9-235573 and JP-A-7-197047, a fuel for diesel engine is produced by reacting a waste edible oil and methanol in the presence of sodium hydroxide. In JP-A-7-197047, transesterification is usually carried out with an alkali catalyst such as sodium hydroxide under the atmospheric pressure at a temperature of 50 to 70xc2x0 C. In this case, a pre-treatment is essential because, when a free fatty acid exists in an oil or fat as a raw material, it reacts with the alkali catalyst to form a soap. In addition, a after-treatment for separation is also required because a small amount of a soap is produced in the course of the transesterification even when the pre-treatment is carried out.
On the other hand, it has been known that, when the transesterification is carried out under conditions of 9 to 10 MPa and 220 to 250xc2x0 C., an oil or fat of a low purity containing free fatty acids can be used as a raw material [Ullmann""s Encyclopedia of Industrial Chemistry, Fifth Completely Revised Edition, Vol. A10 (1987), p. 281].
In addition, in U.S. Pat. No. 5,713,965, a technology is disclosed in which a fuel for diesel engine and a lubricant oil containing fatty acid esters are produced from an oil or fat and an alcohol in the presence of a lipase in a hexane solvent. An example has also been known in which a fatty acid ester is produced from an oil or fat and an alcohol with addition of a catalyst under pressure [Ullmann Enzyclopaedie der Technischen Chemie, Vielte Edition, Vol. 11 (1976), p. 432]. That is, the reaction is carried out with an alkali catalyst or a zinc catalyst under conditions of 10 MPa, 240xc2x0 C. and 7 to 8 times excess of methanol.
A technology has also been known in which fatty acid esters are produced by continuously reacting an oil or fat with an alcohol at 240xc2x0 C. and 9 MPa (90 bar) in the presence of an alkali catalyst [Journal of the American Oil Chemists"" Society, Vol. 61, No. 2(1984)]. Detail of the alkali catalyst, however, is unclear.
Furthermore, a process has been proposed in which the reaction is carried out using sodium carbonate or sodium hydrogen carbonate as a heterogeneous solid catalyst under conditions including the ordinary pressure or a pressure approximately the ordinary pressure at a boiling point of the used alcohol or a temperature approximately such point (JP-A-61-254255). The reaction in this process, however, is slow and thus the productivity is insufficient.
A technology has also been known in which fatty acid esters are produced by reacting an oil or fat with an alcohol within a range of 170 to 250xc2x0 C. at 10 MPa (100 bar) or below in the presence of a catalyst of ZnO or a complex oxide of Zn and Al (U.S. Pat. No. 5,908,946), but the reaction is also slow.
Moreover, a process has been proposed in which a monoglyceride is selectively produced by reacting an oil or fat with an alcohol within a range of 25 to 260xc2x0 C. at a pressure of 0.1 MPa (1 atm) to 10.1 MPa (100 atm) using a solid catalyst containing an alkaline earth metal oxide or the like, but there is no disclosure for a process for producing fatty acid alkyl esters and glycerol.
An object of the present invention is to provide a process for producing a fatty acid ester and glycerol from an oil or fat with an alcohol under more adequate conditions and efficiently and with a high yield, as well as a fuel and others containing the fatty acid ester.
As the result of extensive studies on a process for producing a fatty acid ester and glycerol by reacting an oil or fat with an alcohol and on a fuel containing said fatty acid ester, the present inventors have found the fact that the reaction proceeds with a high yield when the reaction is carried out with addition of a solid base catalyst and under conditions in which the oil or fat and/or the alcohol are/is in a supercritical state exceeding 260xc2x0 C., or when the reaction is carried out with addition of a nickel-containing solid catalyst and under conditions in which the oil or fat and/or the alcohol are/is in a supercritical state, and thus have completed the invention. Therefore, the present invention includes the following features:
[1] A process for producing a fatty acid ester from an oil or fat and an alcohol, wherein the process comprises reacting an oil or fat with an alcohol in the presence of a solid base catalyst under conditions in which at least one of the oil or fat and the alcohol is in a supercritical state at a temperature exceeding 260xc2x0 C.
[2] A process for producing a fatty acid ester from an oil or fat and an alcohol, wherein the process comprises reacting an oil or fat with an alcohol in the presence of a nickel-containing solid catalyst under conditions in which at least one of the oil or fat and the alcohol is in a supercritical state.
[3] A fuel comprising a fatty acid ester obtained by the process according to the above described [1] or [2].
[4] A fuel for diesel engine comprising a fatty acid ester obtained by the process according to the above described [1] or [2].
[5] A base oil for lubricant oil comprising a fatty acid ester obtained by the process according to the above described [1] or [2].
[6] A fuel oil additive comprising a fatty acid ester obtained by the process according to the above described [1] or [2].